This invention generally relates to post-tensioned methods of prestressing architectural structural members; and more specifically, it relates to improved tension-strength for laminated wooden-beams and wooden-columns, and their manufacturing.
Heretofore, several related structural members have been patented which have been variously adapted in the construction of buildings, bridges, mines, tunnels, walls, and the like which consist primarily of concrete. By casting in a manner of tension-rod having opositively threaded ends with tensioning nuts thereon, a company could manufacture a concrete-beam for example; and, because concrete is relatively strong in compression, yet comparatively weak in tension, achieve greatly enhanced structural quality by essentially transfering applied weight bearing loads internally into the pre-tensioned element encased therein. Thus with the concrete medium able to thereby easily withstand the extra beam compression-loading imposed by the special pre-tensioning element therein, it may be readily understood that up to the ultimate compression/burst-strength(radial fracturing relative to the axis of the encased tensioning element) of a given concrete specimen, the beam's useful load-bearing capacity would be manifoldly enhanced via the prestressing (albeit preloading in an opposite resistive manner as it were) technique.
The usefulness of such an improved structural member, which indeed may be throught of as a cousin to the older Pratt-truss(often used in both roof and bridge construction as a primary supporting longeron), is apparent in the substantially lighter architectural designs which have emerged into presense since the inception of this advancement, which is now part of standard international textbook engineering.
A good early example of this technology, is seen in U.S. Pat. No. 1,441,970(filed--June/1920) where the French-inventor devised a clever assembly of bricks, framed by a wooden perimeter, whereby the integrity of a brickwork panel was maintained via a plurality of spaced tensioning-rods(having tightening nuts on each end) which ran both latitudinally and longitudinally(thereby creating an invisible internal gridwork of prestressed tension elements). Not to be outdone, German industrialist Hugo Junkers is shown to have introduced U.S. Pat. No. 1,895,667(filed--March/1929) for a hi-performance composite-metal assemblage as a much more light-weight structural beam like member; albeit a bit complex.
Some 3-decades Later, an American inventor set forth U.S. Pat. No. 3,029,490(filed--November/1954) for an improved "post-tensioning method for pre-stressing members", and some fifteen drawing-figures deal primarily with a simplified method of casting multipul deflected type tensioning-elements therein, in a uniformly spaced manner; thereby enhancing the concrete-beam's performance.
Shortly thereafter, another American inventor claimed U.S. Pat. No. 3,003,217(filed--February/1957) as "an apparatus for manufacturing prestressed concrete members", which again deals primarily with the more effective deflectedly down-draped encased tension-element; and a special method by which to automatically maintain a more consistant degree of tension regardless as to subsequent curing-contraction of the concrete-beam substance.
Most relevant, U.S. Pat. No. 3,251,162(filed--January/1962) shows a laminated-wood beam of prestressed/post-tensioned configuration, wherein the tendon or truss-element is extended entirely to the opposed vertical ends of the various generic beam embodiments disclosed. Also shown are different arrangements for use of transverse/truss-pins, which serve to take-up tensioning load-vectors of the truss-elements. Accordingly, this configuration imposes certain dire installation limitations, which the instant disclosure hereof serves to overcome.
Interestingly, U.S. Pat. No. 4,362,589(filed--November/1981) shows a special automated-mill methodology of making a large fabricated wooded I-beam of tapered configuration, useful in making long-span truss or joists for the floors or ceilings of a building.
Still, be that all as it is, large wooden solid-beams are often an aesthetic preference alternate for many architects. However, in more recent years, because of the general unavailability of larger trees today, and their hi-cost when available, mills have resorted to a very practical if not more effective type of wooden-beam, known as the multiply/laminated-beam.
Accordingly, this instant inventor has devised means by which to likewise further improve the load-bearing performance of modern laminated-beams to surprising advantage, as shall now be set forth; and, is currently being developed under the tradename "TensionTech".TM./laminated-beam via auspices of Saucke-Construction Co./Portland, N. Dak. The first such improved beam was officially installed into this inventor's house back in August of 1987, and is observed to be providing excellent results.